The present invention relates in general to a method for leak testing of a container, to a test chamber therefor and to a test machine for in-line testing of such containers. More particularly, the present invention is directed to a method for reducing test cycle time and for improving the measuring accuracy of a leak testing process as well as to a test chamber and to a test machine with reduced test cycle time and improved measuring accuracy.
Methods for leak testing of containers are known in which a pressure difference is applied between the interior and the exterior of a container to be tested as an initial value for later measuring. Afterwards, the time course of a pressure value, which is dependent from the pressure difference installed as the initial value and from leakage conditions of the container to be tested, is measured, significant for leak conditions of the container under test.
Such a leak testing method is e.g. known from the German laid open print no. 24 47 578. This reference provides for a testing method to test the welding seam of such container with respect to leakage. Therefore such containers are pressure loaded inside and also outside, through an opening of the container to be tested. There is provided separately a test channel around the welding seam of the container and leakage is monitored by measuring the time course or timely development of pressure within said test channel. This measuring is indicative for leakage of the welding seam of the open container.
From the German laid open print no. 21 15 563 it is further known to test the seam of containers which are closed by a foil lid. Thereby, the bottom of the container is perforated by means of a needle-like end part of a pressure line, by which the inside of the container is pressurized. By monitoring the time course of the inside pressure of the container, an indication is provided indicative of tightness of the container.
From the article "Lecksuche mittels Differenzdruckmessungen" from J. T. Furness, VFI 4/78, it is generally known to test a container on leakage by monitoring its internal or its external pressure. Thereby it is described that the smaller that a volume is selected wherein the time course of pressure is monitored, the more accurate such a measuring will become.
There exists a clear need for shortening the time span necessitated for a test cycle of a container on one hand and of improving the accuracy of such tests to be able to detect the smallest leakages of such containers.
A method and test chamber for leak testing a container with a substantially flexible wall portion disclosed in applicants' earlier U.S. Pat. No. 5,042,291 offer a solution to the aforementioned need wherein the container is introduced into a test cavity so that the wall portion of the container is spaced from an inner adjacent wall portion of the test cavity with a gap being defined between the wall portion of the cavity and the flexible wall portion of the container. A pressure difference is installed as an initial value between the interior of the container and at least the gap by applying a pressure at least to the gap which is smaller than a pressure inside the container. The flexible wall portion of the container is supported from its exterior side within the test cavity using a grid or a mesh structured inlay to prevent the flexible wall portion from bending outwardly into contact with the wall portion of the test cavity as a result of the pressure difference. The time course of a pressure prevailing within the gap is measured as a leak indicative signal.